THE INFUSORIA. 99 



vision ; this is generally effected by the formation of a more 

 or less transverse constriction, whereby the body becomes 

 divided into two parts, which separate, each developing those 

 structures which are needed for its completion. The endo- 

 plast, however, always elongates and divides, one portion 

 going along with each product of fission. Neither budding 

 nor longitudinal fission occurs among the free Infusora, the 

 appearances which have been regarded as evidence of these 

 processes being due to the opposite operation of conjugation. 

 M. Balbiani, 1 its discoverer, thus describes the process of conju- 

 gation in Paramecium bursaria : 



" The Paramoeoia assemble in great numbers either tow- 

 ard the bottom or on the sides of the vessel in which they 

 are contained. They then conjugate in pairs, their anterior 

 ends being closely united ; and they remain in this state for 

 five or six days or more. During this period the nucleus and 

 nucleolus become transformed into sexual organs. 



" The nucleolus is changed into an oval capsule, marked 

 superficially by longitudinal striae. Sooner or later, it usually 

 becomes divided into two or four portions, which grow inde- 

 pendently, and form many separate capsules. About the time 

 of separation, each of these is found to be a capsule containing 

 a bundle of curved rods (baguettes), enlarged in the middle, 

 and thinner at the ends. 



" The nucleus also becomes enlarged, and gives rise — in a 

 manner not clearly explained — to small spherical bodies anal- 

 ogous to ovules. 



"It is usually about the fifth or sixth day after conjuga- 

 tion that the first germs appear, as little rounded bodies formed 

 of a membrane which is rendered visible by acetic acid, and 

 of grayish pale homogeneous or almost imperceptibly granu- 

 lar contents, in which, as yet, neither nucleus nor contractile 

 vacuole is distinguishable. It is only later that these organs 

 appear. The observations of Stein and of F. Cohn have 

 shown how these embryos leave the body of the mother un- 

 der the form of Aci?ieta3, provided with knobbed tentacles and 

 true suckers, by uieans of which they remain for some time 

 adherent to her, and nourish themselves from her substance. 

 But their investigations have not disclosed the ultimate fate 

 of the young. 



" I have been able to follow them for a long period after 



» Balbiani, "Note relative a TExistence d'une Generation Sexuelle chez 

 les Inlusoires." (Journal de la Physiologie, tome i., 1858.) 



